Our invention relates to an apparatus, generally known as a disk drive, for reading and/or writing data on a recording disk such as a flexible magnetic disk, or a floppy disk according to common parlance. More specifically, our invention pertains to an apparatus in such a disk drive for centering and clamping the recording disk in a preassigned position for data transfer with a transducer head assembly or a pair of such assemblies.
We are aware of several devices heretofore suggested and used for centering and clamping a flexible magnetic disk in a disk drive. Generally, such devices comprise a clamp in the form of a tapered collet which is both rotatable and movaoble into and out of engagement with a socketed drive hub rigidly mounted on a motor driven shaft. U.S. Pat. No. 3,768,815 to Mathurin teaches the radial splitting of the collet into several segments. The collet segments are wedged apart against the inner wall of the drive hub defining the socket, in order that the magnetic disk may be positively arrested between collet and hub in axial alignment therewith. However, the use of the wedging means, as well as of the clamp and release springs associated with the collet, according to Mathurin makes his apparatus expensive in construction and difficult of assemblage.
An obvious remedy for these weaknesses of Mathurin's apparatus might be to make the maximum diameter of the tapered, segmented collet greater than the diameter of the socket in the drive hub, as disclosed in Japanese Utility Model Publication No. 58-22318 (laid open to public inspection on Dec. 18, 1978). The collet will then pressfit in the socket in the drive hub to firmly clamp the magnetic disk therebetween without the aid of the wedging means that complicate the clamping mechanism.
The two foregoing known devices have a problem in common, however. The problem arises from the fact that the annular disk bearing surface of the drive hub, the substantially annular disk clamping surface of the collet, and the magnetic disk to be clamped therebetween are all not necessarily absolutely flat. In such cases the magnetic disk cannot possibly be clamped firmly enough unless the collet segments are individually resiliently supported.
The concept of resiliently supporting the individual collet segments is not new but has been suggested by Rolph U.S. Pat. No. 4,125,883. Rolph teaches to join the collet segments to the central body of the collet via respective resiliently deflectable fingers. These fingers are set at an angle to the axis of the collet, as well as to a plane normal to the collet axis, in order to give a sufficient amount of deflection. We object to this angular finger arrangement as it adds to the axial dimension of the collet and, in consequence, of the dimension of the complete disk drive in the same direction. It may be contemplated, as an alternative to the noted finger configuration, to dispose the fingers on a plane perpendicular to the collet axis and to make them sufficiently thin to afford a required degree of deflection. This alternative is unsatisfactory, however, as such thin fingers would be easy to break.